1. Field of the Invention
The present invention relates to optical simulation apparatus, and more particularly to an optical simulation apparatus having three relatively movable optical image inputs.
2. Description of the Prior Art
In the field of optical simulation, it is often desirable to provide to an observer images projected at true apparent distances. Display systems which project images to infinity are known in the art; one such system is described in U.S. Pat. No. Re. 27,356 and manufactured by Farrand Optical Co., Inc., as an in-line infinity display system. When a virtual image (or a pluraity of superimposed images) is presented to one side of the infinity display at a distance equal to the local distance of the infinity display the image presented to an observer on the other side appears to be at or near infinity. However, if a virtual image is presented to such an infinity display system at a distance less than the focal length of the system, the observer will perceive that image to be closer than at infinity. This effect is in accordance with the mathematical relationship
a=(f.sup.2 /b)-f,
where
A EQUALS THE APPARENT DISTANCE FROM THE INFINITY DISPLAY SYSTEM OF THE PRESENTED IMAGE AS SEEN BY THE OBSERVER;
B EQUALS THE SEPARATION OF THE PRESENTED IMAGE FROM THE FOCAL PLANE OF THE INFINITY DISPLAY; AND
F EQUALS THE FOCAL LENGTH OF THE INFINITY DISPLAY SYSTEM.
With such an arrangement it is possible to superimpose (by means of a beam splitter, for example) a background image and a foreground image and to present these superimposed images to the infinity display system. By moving the foreground image toward the display system so that it is presented at a distance less than the focal length of the system it appears to an observer to be closer than the background image. Further movement of the foreground image changes the apparent distance of that image.
In other simulation applications, it is desirable to simulate the true relative parallax and apparent distance of a third movable image when viewed in relation to two other relatively movable images. One such application involves the simulation of an inflight air-refueling operation in which a tanker aircraft extends and directs a refueling boom towards an approaching receiver aircraft which is to be refueled. In order to train an operator of the refueling boom to perform the task of directing the boom tip accurately to the receiver aircraft's fueling port on-ground simulation apparatus is desirable so that the operator can become familiar with the dynamic visual cues which are required for the correct performance of the mission.
The present invention in a described embodiment provides simulation apparatus for such an inflight refueling operation in which the trainee observer is not only furnished true stereopsis, but can perceive the true angular sizes of the refueling boom and the receiver aircraft, and also the true relative parallax between the boom and receiver aircraft, and between the receiver aircraft and sky/terrain background.